Menu

Close

Development of the foregut in Katharina tunicata (Mollusca; Polyplacophora)

Brandy S. Biggar

Preprint posted on February 28, 2021 https://www.biorxiv.org/content/10.1101/2021.02.28.433208v1

Say “Aaaah!”. Foregut development and toothed tongues in the black Katy chiton

Selected by Paul Gerald L. Sanchez and Stefano Vianello

Background

With the exception of bivalves (think mussels, scallops, and the sort) all 100000 species of molluscs that exist on our planet use the same structure for feeding: the radula (“little scraper”). This structure is a spikey, toothy, metal-studded “tongue”, through which snails, sea slugs, limpets and other molluscs graze their environment and sweep food into their digestive system.

The radula of the black Katy chiton (Katharina tunicata; Figure 1) is more of a mix between a drill, a chainsaw, and a conveyor belt, with up to 150 rows of mineral-hardened teeth excavating sediment and unearthing food. Developmentally, this structure is formed by outpocketing of the digestive tube of the larva, as the chiton settles to the seafloor to undergo metamorphosis and as its foregut transforms in the various components of the mouth cavity.  

Given the basal position of chitons within the mollusc evolutionary tree, studying the development of their feeding structures can hold important clues  about the life history of ancestral molluscs. Specifically, it is still unclear whether molluscan ancestors first lived their life floating and feeding in water (and then evolved to settle and live on the seabed), or whether they existed as seabed-dwellers that then evolved non-feeding larval forms, living in suspension. In this second scenario, the presence of feeding structures in the larvae would be a secondary evolutionary innovation and studies of basal species such as chitons can help resolve the directionality of such evolutionary changes.

 

Katharina tunicata post-metamorphic juveniles on encrusting coralline red algae

FIGURE 1:  Katharina tunicata post-metamorphic juveniles on encrusting coralline red algae A, B) 1 day post metamorphosis (dpm), C) 3 dpm, D) 14 dpm and E, F) 36 dpm. (from Figure 16 of the preprint, reproduced under CC-BY 4.0)

 

Key findings

This preprint combines external descriptions of Katharina tunicata development, and histology sectioning documenting important changes in internal anatomical features. Specific attention is given to foregut development, from larval stages to juvenile stages, through metamorphosis (Figure 2). Notably:

  • The author documents the presence of a differentiating buccal mass and radula already at 10 days post hatching. After one week, a radular rudiment and radular teeth can be observed in the larva.
  • As the larva settles on the seabed and undergoes metamorphosis into its armored juvenile form, the author describes the unique chiton process of biomineralisation of the radular teeth, which get capped with magnetite (!), and times this to occur at 14 days post-metamorphosis.

 

Katharina tunicata development and foregut ontogenesis through metamorphosis

FIGURE 2: Katharina tunicata development and foregut ontogenesis through metamorphosis. DPH: days post-hatching, DPM: days post-metamorphosis;  at: apical tuft; pr: prototroch, mt (or m): mouth; mg: midgut; bm: buccal mass; rr: radular rudiment; ne: neuropil; sv: shell valves; es: esophagus, mc: magnetite caps; rd: radula (adapted from preprint, reproduced under CC-BY 4.0)

 

Significance

This preprint provides detailed descriptions of internal anatomical changes in a Polyplacophoran species, going beyond simple external observation. Specifically, it provides a description of foregut development before, during, and after metamorphosis, leveraging the evolutionary position of this animal to provide insight on the possible features of ancestral molluscs.

Of note is the documentation of feeding structures (radula, buccal mass) already at the larval stage, even though Katharina tunicata larvae are non-feeding and rely on the yolk provided by the mother. If the black Katy chiton indeed preserves features of the common mollusc ancestor, the evidence gathered by this study supports a so-called “intercalation theory” of mollusc evolution whereas feeding larvae would be a secondary innovation and ancestral molluscs would have been seafloor dwellers. 

 

Questions to the author

  1. What does working with chitons look like in practice? Do you raise larvae in the lab?
  2. Why would a planktonic lifestyle favour evolvability of the foregut? Are there evolutionary pressures that would push a larva feeding on material yolk to develop structures to feed autonomously? 
  3. If a seafloor-dwelling lifestyle with non-feeding larvae was the ancestral condition, what would have pushed current planktonic mollusc species to abandon this lifestyle?
  4. Could you elaborate on the modularity of radulae in chitons and polyplacophorans? You mention that the chiton radula has a mix of features of other species.
  5. In e.g. mice and humans the foregut also originates the respiratory system. Is this the case also in molluscs?

 

Further reading

Page, L.R., and Hookham, B. 2017. The gastropod foregut- evolution viewed through a developmental lens. CJZ Virtual Spec. Issues 01:227–238.

Page, L.R. 2009. Molluscan Larvae: Pelagic juveniles or slowly metamorphosing larvae? Biol. Bull. 216:216–225.

iNaturalist entry of the Black Katy chiton: https://www.inaturalist.org/taxa/47632-Katharina-tunicata 

Tags: chiton, foregut, radula

Posted on: 6th April 2021

doi: Pending

Read preprint (1 votes)




Have your say

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Sign up to customise the site to your preferences and to receive alerts

Register here

preLists in the developmental biology category:

EMBL Synthetic Morphogenesis: From Gene Circuits to Tissue Architecture (2021)

A list of preprints mentioned at the #EESmorphoG virtual meeting in 2021.

 



List by Alex Eve

EMBL Conference: From functional genomics to systems biology

Preprints presented at the virtual EMBL conference "from functional genomics and systems biology", 16-19 November 2020

 



List by Jesus Victorino

Single Cell Biology 2020

A list of preprints mentioned at the Wellcome Genome Campus Single Cell Biology 2020 meeting.

 



List by Alex Eve

Society for Developmental Biology 79th Annual Meeting

Preprints at SDB 2020

 



List by Irepan Salvador-Martinez, Martin Estermann

FENS 2020

A collection of preprints presented during the virtual meeting of the Federation of European Neuroscience Societies (FENS) in 2020

 



List by Ana Dorrego-Rivas

Planar Cell Polarity – PCP

This preList contains preprints about the latest findings on Planar Cell Polarity (PCP) in various model organisms at the molecular, cellular and tissue levels.

 



List by Ana Dorrego-Rivas

Cell Polarity

Recent research from the field of cell polarity is summarized in this list of preprints. It comprises of studies focusing on various forms of cell polarity ranging from epithelial polarity, planar cell polarity to front-to-rear polarity.

 



List by Yamini Ravichandran

TAGC 2020

Preprints recently presented at the virtual Allied Genetics Conference, April 22-26, 2020. #TAGC20

 



List by Maiko Kitaoka, Madhuja Samaddar, Miguel V. Almeida, Sejal Davla, Jennifer Ann Black, Dey Lab

3D Gastruloids

A curated list of preprints related to Gastruloids (in vitro models of early development obtained by 3D aggregation of embryonic cells). Preprint missing? Don't hesitate to let us know.

 



List by Paul Gerald L. Sanchez and Stefano Vianello

ASCB EMBO Annual Meeting 2019

A collection of preprints presented at the 2019 ASCB EMBO Meeting in Washington, DC (December 7-11)

 



List by Madhuja Samaddar, Ramona Jühlen, Amanda Haage, Laura McCormick, Maiko Kitaoka

EDBC Alicante 2019

Preprints presented at the European Developmental Biology Congress (EDBC) in Alicante, October 23-26 2019.

 



List by Sergio Menchero, Jesus Victorino, Teresa Rayon, Irepan Salvador-Martinez

EMBL Seeing is Believing – Imaging the Molecular Processes of Life

Preprints discussed at the 2019 edition of Seeing is Believing, at EMBL Heidelberg from the 9th-12th October 2019

 



List by Dey Lab

SDB 78th Annual Meeting 2019

A curation of the preprints presented at the SDB meeting in Boston, July 26-30 2019. The preList will be updated throughout the duration of the meeting.

 



List by Alex Eve

Lung Disease and Regeneration

This preprint list compiles highlights from the field of lung biology.

 



List by Rob Hynds

Young Embryologist Network Conference 2019

Preprints presented at the Young Embryologist Network 2019 conference, 13 May, The Francis Crick Institute, London

 



List by Alex Eve

Pattern formation during development

The aim of this preList is to integrate results about the mechanisms that govern patterning during development, from genes implicated in the processes to theoritical models of pattern formation in nature.

 



List by Alexa Sadier

BSCB/BSDB Annual Meeting 2019

Preprints presented at the BSCB/BSDB Annual Meeting 2019

 



List by Dey Lab

Zebrafish immunology

A compilation of cutting-edge research that uses the zebrafish as a model system to elucidate novel immunological mechanisms in health and disease.

 



List by Shikha Nayar

Also in the evolutionary biology category:

EMBL Synthetic Morphogenesis: From Gene Circuits to Tissue Architecture (2021)

A list of preprints mentioned at the #EESmorphoG virtual meeting in 2021.

 



List by Alex Eve

Planar Cell Polarity – PCP

This preList contains preprints about the latest findings on Planar Cell Polarity (PCP) in various model organisms at the molecular, cellular and tissue levels.

 



List by Ana Dorrego-Rivas

TAGC 2020

Preprints recently presented at the virtual Allied Genetics Conference, April 22-26, 2020. #TAGC20

 



List by Maiko Kitaoka, Madhuja Samaddar, Miguel V. Almeida, Sejal Davla, Jennifer Ann Black, Dey Lab

ECFG15 – Fungal biology

Preprints presented at 15th European Conference on Fungal Genetics 17-20 February 2020 Rome

 



List by Hiral Shah

COVID-19 / SARS-CoV-2 preprints

List of important preprints dealing with the ongoing coronavirus outbreak. See http://covidpreprints.com for additional resources and timeline, and https://connect.biorxiv.org/relate/content/181 for full list of bioRxiv and medRxiv preprints on this topic

 



List by Dey Lab, Zhang-He Goh

1

SDB 78th Annual Meeting 2019

A curation of the preprints presented at the SDB meeting in Boston, July 26-30 2019. The preList will be updated throughout the duration of the meeting.

 



List by Alex Eve

Pattern formation during development

The aim of this preList is to integrate results about the mechanisms that govern patterning during development, from genes implicated in the processes to theoritical models of pattern formation in nature.

 



List by Alexa Sadier
Close